In modern communications, data signals are being transmitted through the air continuously. Those data signals are received at a variety of amplitudes. Consequently, receivers must be able to process data signals of varying received signal strength. Therefore, many modern hi-tech receivers contain amplifiers that produce variable gain amplification outputs. Such amplifiers are aptly called variable gain amplification amplifiers. A “dual gain amplification” amplifier is a specific kind of variable gain amplification amplifier that produces a high gain amplification output and a low gain amplification output. Amplifiers of this nature are usually included in a receiver to provide gain amplification to the data signal at the beginning (or front end) of the receive circuit. However, when the data signal is amplified, any noise introduced in the received signal will also be amplified and propagated through the receive chain circuitry. Consequently, amplifiers in the receiver are usually designed to provide very low noise and are often referred to as low-noise amplifiers, or LNAs.
LNAs, like all other amplifiers, suffer from a phenomenon called signal compression. Signal compression is the phenomenon of limiting gain amplification. Because of the physical characteristics of transistors, or other elements in the LNA, a signal cannot be infinitely amplified. There is a point at which amplification begins to reach saturation. That point is referred to as the 1 dB compression point, or “P1dB”. FIG. 1A is an illustration demonstrating the principle of 1 dB compression caused by an amplifier. Referring to FIG. 1A, signal compression can be seen when the gain amplification output of an amplifier (Pout) stops having a linear relation to the input signal (Pin), and begins to saturate. P1dB is the point at which Pout deviates from a linear increase with Pin, and begins to “compress” towards a saturation level (Psaturated).
One particular problem, however, with modern dual-gain amplification amplifiers is that they produce a P1dB for low gain amplification that is much lower than the P1dB for high gain amplification. FIG. 1B is an illustration of two signals; one signal receiving a high gain amplification and the other signal receiving a low gain amplification, with corresponding P1dBs according to the prior art. Prior art dual-gain amplification LNAs produce results as shown in FIG. 1B wherein during low gain amplification, the data signal will begin to experience signal compression sooner than it would than during high gain amplification. It would be advantageous, however, to maintain the same high P1dB for low gain amplification as for high gain amplification.
Some prior art devices have attempted to stabilize P1dB for high and low gain amplification by utilizing an attenuation circuit (also called a mismatch circuit) in the receiver to attenuate the incoming data signal. However, a mismatch circuit introduces excessive noise, thus leading to a very noisy LNA.
Consequently, it would be advantageous to have a dual-gain amplification LNA that maintains the same P1dB for low gain amplification as for high gain amplification without introducing excessive mismatch circuit noise or without causing the P1dB for the overall circuit to suffer.